Trans-delta-9-tetrahydrocannabinol (THC), the active ingredient in marijuana, is being evaluated for toxicity and carcinogenicity in F344 rats and B6C3F1 mice. All interim evaluation is scheduled at 65 weeks and includes hematology, clinical chemistry, and an evaluation of toxicity to the reproductive system. Final laboratory reports for the rat and mouse studies are scheduled for submission in 3/91 and 12/90, respectively. Results of these studies will provide information about the toxicity of chemicals in experimental animals, information which can be used to help predict possible hazard to humans.